1. Field of the Invention
The present invention relates to a vehicular steering system which provides for steering of both the front and rear wheels.
2. Description of Relevant Art
A vehicular steering system which provides for steering of both the front and rear wheels by operation of a steering wheel is advantageous in that the disagreement between the vehicle direction and the tangential direction of the turning locus, which occurs when only the front wheels are steered, can be eliminated and in that the difference in generation timing between a lateral force produced in the front wheels and that in the rear wheels can also be eliminated. In such a type of steering system, however, a resultant force of an external force acting on the front wheels from the road surface plus an external force acting on the rear wheels from the road surface at the time of steering operation for both wheels acts as a reaction force against the operation of a steering wheel, and consequently it becomes necessary for the vehicle driver to impart a steering torque greater than such reaction force to the steering wheel, thus resulting in a larger steering torque than that in the ordinary type of vehicles wherein only front wheels are steered. This inconvenience can be eliminated by mounting on the vehicle a power steering system equipped with an auxiliary power means such as a power cylinder for assisting the vehicle driver in operating the steering wheel. However, because the conventional power steering systems provide for steering of the front wheels only, the steering operation for the rear wheels through the steering wheel is not assisted at all. As a solution to this problem, it has been considered to provide the vehicle with a power steering system for the front wheels and one for the rear wheels separately. But if an auxiliary power means is attached to each of the front and rear wheel steering mechanisms, the number of associated parts increases substantially, thus causing inconveniences such as an increase in weight and cost of the vehicle. Such a separate provision of two auxiliary power means is further disadvantageous in that an appropriate auxiliary power according to a resultant force of an external force acting on the front wheels from the road surface plus an external force acting on the rear wheels from the road surface at the time of steering both wheels is not transmitted to the steering wheel.
For steering both front and rear wheels by operation of the steering wheel, it is necessary to adopt a structure wherein a rear wheel steering mechanism is connected to a front wheel steering mechanism to which is transmitted a steering torque of the steering wheel, and the rear wheel steering mechanism is operated along with operation of the front wheel steering mechanism to steer the rear wheels. To this end, the front and rear wheel steering mechanisms are connected through a connection path. In this case, from the standpoint of simplification of structure, it is desirable to constitute the connection path as a rectilinear path by a single shaft or the like. But such a rectilinear configuration is not desirable from the standpoint of working efficiency because the connection path projects into the interior space of the vehicle, thus making the interior space narrower, and because it becomes necessary to perform assembling and mounting operations for the connection path within the interior of the vehicle. Moreover, the connection structure between the front wheel steering mechanism and the connection path or between the connection path and the rear wheel steering mechanism must attain a smooth operation of the front or rear wheel steering mechanism. Furthermore, it is desired that such connection structure permit any desired setting of a steering angle of the rear wheels relative to the front wheels and also permit easy mounting.
Additionally, both a steering shaft which is connected to the steering wheel and the connection path are connected to the front wheel steering mechanism, and it is desirable that the connection path be connected to the front wheel steering mechanism in a position away from the steering shaft to avoid its interference with the steering shaft.
The present invention effectively overcomes the aforementioned inconveniences and drawabacks associated with the conventional vehicular steering systems.